This invention relates to a variable venturi type carburetor. In conventional carburetors an electromagnetic valve is used to change over between an internal passage leading to the suction pipe intake passage downstream of the air cleaner and an external passage leading to a unit outside the carburetor. During the engine operation the fuel vapor in the float chamber is conducted to the internal passage, and to the external passage when the engine is not running. However, the electromagnetic valve presents difficulties in making the carburetor small and light. Thus carburetors employing an electromagnetic valve are necessarily expensive.